(a) Field of the Invention
The present invention relates to a liquid crystal display, and in particular, to a liquid crystal display with color characteristic compensation and response time compensation and a driving method thereof.
(b) Description of Related Art
Flat panel displays such as liquid crystal displays (LCDs) have been developed and substituted for cathode ray tubes (CRTs) since they are suitable for recent personal computers and televisions, which become lighter and thinner.
An LCD representing the flat panel displays includes a liquid crystal panel assembly including two panels provided with two kinds of field generating electrodes such as pixel electrodes and a common electrode and a liquid crystal layer with dielectric anisotropy interposed therebetween. The variation of the voltage difference between the field generating electrodes, i.e., the variation in the strength of an electric field generated by the electrodes changes the transmittance of the light passing through the LCD, and thus desired images are obtained by controlling the voltage difference between the electrodes. A typical LCD includes thin film transistors (TFTs) as switching elements for controlling the voltages to be applied to the pixel electrodes, and a plurality of display signal lines for transmitting signals to be applied to the TFTs.
The LCD has been currently applied for notebook computers, and extending its usage for desktop computers. Contemporary computer users have desires of watching moving pictures on a computer display device under the advanced multimedia environment. In order to satisfy such desires, it is required to enhance the color characteristic and the response time of the LCD.
Accurate color capture (ACC) is a known technique for enhancing the color characteristic.
An LCD receives red, green and blue (RGB) data from an external graphic source. The RGB data represent values of data voltages to be applied to the corresponding pixels of the LCD. The bit number of the RGB data relates to the number of grays of the data voltages. The N bit RGB data can represent 2N grays, and thus the number of the grays is limited by the bit number of the input RGB data. Therefore, the bit number of the input RGB data should be increased for increasing the number of the grays. However, the increase of the bit number of the input RGB data makes the system complicated and the frequency of the system clock increased.
The ACC technique is capable of increasing the number of the grays without increasing the bit number of the input RGB data. For example, a frame rate control (FRC) is used for displaying grays between two arbitrary gray.
The FRC expands one frame into several frames. For instance, a pixel of an LCD can display the gray of ‘118.5’ between the two adjacent grays of ‘118’ and ‘119’ by displaying ‘119’ in a frame and displaying ‘118’ in the next frame. After all, the grays of ‘118’ and ‘119’ displayed in two sequential frames are time-averaged to be seen as the gray of ‘118.5’. The number of the frames required for FRC depends upon the number of divisions between the two grays.
Dynamic capacitance capture (DCC) is a known technique for enhancing the response time of the LCD.
The DCC compares an image data in a previous frame and an image data in a current frame for a given pixel and modifies the current data such that the difference between the modified current data and the previous data is larger than that between the original current data and the previous data.
When a voltage is applied to a given pixel, a reasonable time is consumed for the liquid crystal molecules to fully respond thereto. However, the time period given to the pixel may be too short for the liquid crystal molecules to fully respond to the applied voltage since the time period for one frame is nearly fixed at about 16.7 msec. The DCC enhances the response time of the liquid crystal molecules. For example, when the image data in the previous frame is ‘118’ and the original image data in the current frame is ‘128,’ the modified current data has a value greater than ‘128’ such as ‘135’.
The DCC requires a frame memory for storing the data in the previous frame. The modification factors may be stored in a lookup table as function of the previous data and the current data. The size of the lookup table depends on the bit number of the two data to be compared with and increases as the bit number is increased. Therefore, the bit number of the data stored in the frame memory is usually smaller than the bit number of the input RGB data.